leetcode 278. First wrong version

278. First wrong version

Thought analysis ：
Binary search template ！

AC Code ：

class Solution {
    
public:
    int firstBadVersion(int n) {
    
        int l = 1, r = n;
        while(l < r) {
    
            int mid = (long long)l + r >> 1;
            if(isBadVersion(mid)) r = mid;
            else l = mid + 1;
        }
        return r;
    }
};